Welding apparatus and techniques for elevated pierce current

ABSTRACT

An apparatus may include a power supply to generate an output current. The apparatus may further include a plasma torch to apply the output current across a gap and a user interface to receive a selection for enabling a pierce current mode. The apparatus may further include a controller to temporarily increase an output current setting at the plasma torch from a first level to a second level, responsive to the selection of pierce current mode.

This application is a continuation of U.S. application Ser. No.15/626,593, filed Jun. 19, 2017, the contents of which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present embodiments are related to power supplies for welding typepower, that is, power generally used for cutting, welding or heating.

BACKGROUND

Plasma arc cutting is a known technique for cutting metallic materials,such as steels, aluminum, and the like. A plasma arc apparatus mayinclude a plasma arc torch used to generate an arc of sufficient powerto cut a material having a given thickness. In known plasma torchoperations, a cut may be performed by initiating a cut along an edge ofa workpiece. Such cuts may be appropriate for separating one section ofa metal plate from an adjacent section. Alternatively, a plasma torchoperation may be initiated by piercing through a metal plate toestablish an isolated hole. From this point, a cutting operation mayremove a section, such as a circular section from within a larger plate.

At a given amperage applied to a workpiece, a plasma torch may be ableto cut a thicker material of a given metal (from the side) than can bepierced in a hole. For cutting a metal at these thicknesses, the cutaccordingly needs to begin at the edge of the material being cut. Thisfactor limits the applications for a given power supply and precludesthe possibility of cutting holes in the given material at that power.

With respect to these and other considerations, the present disclosureis provided.

BRIEF SUMMARY

In one embodiment, an apparatus may include a power supply to generatean output current. The apparatus may further include a plasma torch toapply the output current across a gap and a user interface to receive aselection for enabling a pierce current mode. The apparatus may furtherinclude a controller to temporarily increase an output current settingat the plasma torch from a first level to a second level, responsive tothe selection of pierce current mode.

In another embodiment, a method of cutting a workpiece may includereceiving a signal indicating a cut current setting corresponding to avalue of output current at a first level for a plasma torch. The methodmay further include receiving an indication that a pierce current modeis enabled, and sending a first control signal to increase the value ofoutput current for the plasma torch from the first level to a secondlevel.

In a further embodiment, an apparatus to control a plasma cuttingoperation may include a power supply to generate an output current. Theapparatus may further include a plasma torch to apply the output currentacross a gap. The apparatus may also include a controller arranged to:set the output current to a zeroth level for arc initiation; increasethe output current to a temporary second level for a predeterminedduration of five second or less; and subsequently decrease the outputcurrent to a steady state cutting current for a balance of the plasmacutting operation.

DESCRIPTION OF FIGURES

FIG. 1 presents an apparatus for plasma cutting, according to variousembodiments of the disclosure.

FIG. 2 presents a user interface according to embodiments of thedisclosure.

FIG. 3 presents a process flow according to embodiments of thedisclosure.

DESCRIPTION OF EMBODIMENTS

Various embodiments provide components and techniques for improvedoperation of a plasma cutting apparatus. In particular, the presentembodiments take advantage of the fact that power supplies foroperations such as plasma cutting may be limited by the thermalload/cycling on the components of the power supply. This considerationleads to a duty cycle rating, e.g. 100% at 40 Amperes (40 A), 80% at 60A, 40% at 100 A. A given power supply may limit its output poweraccording to the duty cycle, which duty cycle may be determined foroperation over periods of time, such as several minutes. This limitationmay unduly limit the current that is output by a plasma torch forcutting, since this may prevent operation at current levels needed topierce a given material. Notably, in the present embodiments, thecurrent output may be increased for a period of time during an initialoperation that does not cause the components to exceed thermalload/cycling, allowing thicker materials to be cut in a piercingoperation. If this “pierce current” is not too much in excess of thenominal cutting current, the consumable life will not be greatlyadversely affected by such operation.

FIG. 1 illustrates an apparatus 100, according to various embodiments ofthe disclosure.

The apparatus 100 may be configured to receive power, such as AC powerfrom an AC supply 102, as shown. The AC supply 102 may provide, forexample, 120 VAC power, or 208-230 VAC power. The embodiments are notlimited in this context. The apparatus 100 may further include an inputrectifier 104 as well as an inverter 106, to generate output current forcutting according to known principles. For example, an output of theinverter 106 may be provided to a workpiece 112 via an outputtransformer 108. The apparatus 100 may be rated to deliver a maximumoutput current via the plasma torch 114. The maximum output current maybe set according to the duty cycle for operation of the apparatus 100.For example, at a 40% duty cycle the maximum output current may be 60 A,80 A or other value. The embodiments are not limited in this context. Asused herein, the term “duty cycle” may refer to the percentage time thatthe apparatus 100 is operated at high output current, such as 60 A, overa period of minutes. For example, a 40% duty cycle may correspond tooperating the apparatus 100 at high output current for cutting for aperiod of 4 minutes, while not operating for six minutes. This operationat 40% duty cycle may be continued where cutting at 60 A output currenttakes place for 40% or less total time.

The apparatus 100 may further include a current sensor, shown as sensor110, which may measure output current on the secondary side of theapparatus 100, as shown. The sensor 110 may provide real timemeasurement of output current, which measurement may be used to controloperation of the apparatus 100. In operation, the apparatus 100 may belimited to a maximum output current, at least for long durationsspanning times greater than several seconds. The maximum output currentmay determine the maximum thickness of a material for workpiece 112 thatcan successfully be cut by the plasma torch 114.

In various embodiments, the apparatus 100 may further include a piercecurrent controller 116, which component may be embodied in a combinationof software and hardware according to embodiments of the instantdisclosure. For cutting operations where a workpiece is a metal plateand where cutting of the workpiece proceeds from the edge of workpiece112, the maximum thickness of workpiece 112 that can be cut may begreater than for cutting operations where the workpiece 112 is to beinitially pierced in the middle of the workpiece 112. For example, 60 Acurrent may be effective for cutting a ¾″ metal plate from the edge,while 60 A may be able to pierce a hole through just ½″ metal plate, andmay be ineffective to pierce a hole through a ¾″ metal plate.

In order to address the above issue, the pierce current controller 116is provided with the capability to adjust the output current foroperating apparatus 100, at least for a short duration, such as on theorder of several seconds or less. In various embodiments, the piercecurrent controller 116 may control components of the apparatus 100, suchas the inverter 106, to facilitate operation at a higher output currentthan the output current set for cutting operation of the apparatus 100.By allowing the operating at a higher output current for short periodsof time, a “pierce current” may be delivered by the plasma torch 114that exceeds a set output current, such as 60 A, at least for a durationsufficient to pierce a hole in the workpiece 112. As an example, apierce current of 90 A may be enabled by the pierce current controller116, so that up to 90 A may be delivered to the plasma torch 114 for aperiod of one second, facilitating the ability to pierce a hole in a ¾″metal plate, as represented by workpiece 112. Subsequently, the outputcurrent may be limited to 60 A, for example, for continued cutting ofthe workpiece 112, which cutting may proceed for a duration of minutes.In other words, once a hole is established in the workpiece 112, thecutting of workpiece 112 may proceed at a lower current level thanneeded to establish the hole. In this manner, a cut in workpiece 112 maybe generated that is entirely formed while not cutting the workpiece 112from the side, while not exceeding the rated output current for theapparatus 100. Because the duration of elevated pierce current islimited to less than several seconds, as an example, the total averagecurrent for a cutting operation lasting several minutes may beapproximately the same as in the case where 60 A current is neverexceeded.

As also shown in FIG. 1 , the apparatus 100 may include a user interface118, where the user interface 118 may include a screen, dial, or otherdevice, providing a display, a selectable menu, or other known interfacefor a user to engage. One embodiment of a user interface 118 isdiscussed below with respect to FIG. 2 . The user interface 118 mayallow a user to select parameters for operation of the apparatus 100,including different modes of operation. As an example, the userinterface 118 may provide for selection of whether to operate theapparatus 100 to allow for increased pierce current, where the outputcurrent may exceed the normal output current for a limited duration.

Turning now to FIG. 2 , an embodiment of the user interface 118 isshown, where the user interface 118 may be embodied as a menu, such as amenu on a display. A PIERCE CURRENT ENABLE component 202 is providedthat allows a user to enable operation of the apparatus 100 in a piercecurrent mode, that is, in a mode providing for increased output current.When selected, the PIERCE CURRENT ENABLE component 202, in conjunctionwith the pierce current controller 116, may set the maximum outputcurrent that can be generated by the inverter 106 from a first level tosecond level. As an example, the first level of output power maycorrespond to 60 A for operating the plasma torch 114 to performcontinuous cutting over a duration up to several minutes. A second levelof maximum output power may correspond to 90 A, for operating the plasmatorch 114 for a short duration, such as several seconds or less. In someexamples the second level may be a predetermined level. This operationmay be appropriate for generating a hole within the workpiece 112, forexample, where 60 A current may be insufficient power for the plasmatorch 114 to penetrate a hole through the workpiece 112.

As also shown in FIG. 2 , the user interface 118 may include a PIERCECURRENT LIMIT component 204, where a user may enter a value of maximumoutput current when pierce current is enabled. For example, if 60 Arepresents the normal output current, the PIERCE CURRENT LIMIT component204 may permit a user to enter values of output current in excess of 60A, up to a determined maximum or limit. Thus, a user may enter “70 A” or“80 A” as an example. Subsequently, the pierce current controller 116may limit output current during a pierce current operation to the valueof current selected by the user. In other embodiments, if pierce currentoperation is enabled, the pierce current controller 116 mayautomatically set an output current for operation in pierce currentmode, such as 90 A, without additional input from a user.

In some embodiments, the user interface may also provide othercomponents (i.e., configuration parameters), such as a CUT CURRENT LIMITcomponent 206, which component allows a user to manually select anoutput current for sustained cutting, such as 60 A. Once set, theinverter 106 may limit output current to 60 A for extended duration,such as over several minutes. In some embodiments, once the value of cutcurrent is selected, a value of pierce current may be generatedaccordingly. Thus, if 60 A is set for cut current, a pierce current,that is, an output current for a short duration, may be set at 90 Aautomatically without user intervention.

As further shown in FIG. 2 , the user interface 118 may include aTHICKNESS SELECT component 208 component. When a user engages theTHICKNESS SELECT component 208, the user may enter a thickness of theworkpiece 112 to be cut. Based upon the thickness selected, the piercecurrent controller 116 may set a limit for output current for cuttingfor an extended duration, such as 60 A, while also setting the piercecurrent, such a 90 A, all without additional user input.

As additionally shown in FIG. 2 , the user interface 118 may include aPIERCE CURRENT DURATION component 210, which allows the duration ofoperation at a higher output current to be manually selected. In someexamples, a user may select different durations up to a maximumduration, such as ½ second, 1 second, 2 seconds, and so forth.

In operation, when pierce current mode is enabled the pierce currentcontroller 116, in conjunction with the inverter 106, may limit outputcurrent at the plasma torch 114 as follows. When a plasma cuttingoperation is to be performed a plasma gas may be flowed to the apparatus100, while a pilot current at relatively low value is established togenerate a plasma arc. At a subsequent moment when the plasma torch 114is applied to a workpiece 112, the output current may be increased tocut the workpiece, while the output current is limited by control of theinverter 106 to a pierce current value, such as 90 A. In other words,during a predetermined period, the inverter 106 may be controlled bypierce current controller 116 to limit output current at the plasmatorch 114 to up to a value of 90 A. For example, the sensor 110 mayprovide real time output current information to the pierce currentcontroller 116 to control operation of the inverter 106, so that outputcurrent does not exceed 90 A. Moreover, the duration where outputcurrent is limited to 90 A may be preset, so that once an initial periodof operation of the plasma torch 114 has elapsed, the output current maybe limited to a lower value. For example, after one second, the piercecurrent controller 116 may then control the inverter 106 to limit outputcurrent to a default output current, such as 60 A, for an extendedduration, such as several minutes.

Thus, with pierce current mode enabled, a given cutting operation mayinvolve two distinct intervals, where during an initial interval ofseveral seconds or less, a relatively higher output current may begenerated, while during a following interval of up to several minutes, arelatively lower output current may be generated. Because the apparatus,such as apparatus 100 may operate for short intervals at an increasedcurrent above a current level sustainable for long term cutting, thepiercing of holes in otherwise uncuttable materials may be accomplished.

While in aforementioned embodiments, an apparatus may include aninterface or other mechanism for enabling a pierce current mode, inadditional embodiments a plasma cutting apparatus may be arranged toautomatically provide a pierce current operation, while not requiringany particular mode to be enabled. For example, an apparatus may includea controller arranged to set the output current to a zeroth level forarc initiation and/or piloting, and to increase the output current to atemporary second level for a predetermined duration of five second orless, and to subsequently decrease the output current when thepredetermined interval (duration) has elapsed to a steady state cuttingcurrent for a balance of the plasma cutting operation. All of theseoperations may be automatically initiated in sequence by the controllerin the absence of selection of an operating mode.

FIG. 3 depicts an exemplary process flow 300, according to embodimentsof the disclosure. At block 302, a selection of cut current is received.The cut current may correspond to the output current to be delivered toa plasma torch over an extended period of time, such as up to manyminutes. The selection of cut current may be received through a userinterface, such as a dial, a touch screen, a keypad, or other device.The flow then proceeds to block 304.

At block 304 a determination is made as to whether pierce current modeis enabled. In various embodiments, enabling of pierce current mode maybe accomplished via a user interface, such as a touch screen, keypad,dial, or other indicating device. If not enabled, the flow proceeds toblock 310, where the output current is limited to the cut current. Atblock 304, if pierce current mode is enabled, the flow proceeds to block306.

At block 306, a determination is made as to whether a pierce currentlimit, meaning a maximum value for pierce current, has been received,such as through a user interface. If not, the flow proceeds to block312, where the cut current value is overridden for a preset duration andat a preset current limit that is greater than the cut current limit.For example, if a cut current is received that is 60 A, and piercecurrent is enabled without indication of any specific value, a presetlimit of 90 A for pierce current may be set as the output current fortwo seconds as a default period. After the two seconds, the outputcurrent (cut current) may be limited to 60 A for the balance of timeused for a cutting operation. If a pierce value has been received, theflow proceeds to block 308.

At block 308 a determination is made as to whether a pierce current timeor duration has been received, such as through a user interface. If not,the flow proceeds to block 314, where the cut current value isoverridden for a preset duration at the received pierce current limit.For example, if a pierce current value received is 80 A, a presetduration for providing 80 A of pierce current may be set as two secondsas a default period. After the two seconds, the output current (cutcurrent) may be limited to 60 A for the balance of time used for acutting operation. If a pierce current time selection has been received,the flow proceeds to block 316, where the cut current value isoverridden for the received duration of pierce current at the valuereceived for pierce current limit.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Thus, the claims setforth below are to be construed in view of the full breadth and spiritof the present disclosure as described herein.

What is claimed is:
 1. An apparatus, comprising: a power supply togenerate an output current; a plasma torch to apply the output currentacross a gap; a controller to temporarily increase the output currentfrom a first level to a second level, wherein the first level issufficient to cut a given material, and wherein the second level isgreater than the first level and is sufficient to pierce the givenmaterial; and a user interface, wherein the user interface comprises aPIERCE CURRENT ENABLE selection operative to enable the power supply togenerate output current up to values corresponding to the second level,and wherein the user interface comprises a selection for THICKNESS ofthe given material, and the controller is operative to set the firstlevel and the second level based on a selected thickness of the givenmaterial.
 2. The apparatus of claim 1, the controller operative to setthe output current to the second level for an initial period, and to setthe output current to the first level for a subsequent periodimmediately following the initial period.
 3. The apparatus of claim 2,the first level comprising an output current for a cutting operationover a duration greater than five seconds.
 4. The apparatus of claim 2,the second level comprising an output current to be applied during theinitial period, wherein the initial period has a duration of two secondsor less.
 5. The apparatus of claim 1, wherein the first level of theoutput current is based upon a duty cycle for operation of the plasmatorch.
 6. The apparatus of claim 1, wherein the user interface comprisesa selection for PIERCE CURRENT DURATION for setting a duration foroperation at the second level.
 7. The apparatus of claim 1, wherein theuser interface comprises a selection for PIERCE CURRENT LIMIT forsetting a maximum current at the second level.
 8. An apparatus,comprising: a power supply to generate an output current; a plasma torchto apply the output current across a gap; and a controller totemporarily increase the output current from a first level to a secondlevel, wherein the first level is sufficient to cut a given material,and wherein the second level is greater than the first level and issufficient to pierce the given material, wherein the second level is setaccording to the first level automatically without user intervention. 9.An apparatus to control a plasma cutting operation, comprising: a powersupply to generate an output current; a plasma torch to apply the outputcurrent across a gap; and a controller arranged to: set the outputcurrent to a zeroth level for arc initiation; increase the outputcurrent from the zeroth level to a temporary second level for apredetermined duration of five seconds or less; and subsequentlydecrease the output current to a steady state first level cuttingcurrent for a balance of the plasma cutting operation, wherein thesteady state first level cutting current is sufficient to cut a givenmaterial, and wherein the temporary second level is greater than thesteady state first level cutting current and is sufficient to pierce thegiven material, and wherein the temporary second level is set higherthan an output current associated with a predetermined duty cycle of theapparatus when the apparatus is set to output the steady state firstlevel cutting current.
 10. The apparatus of claim 9, further comprising:a user interface to receive a selection for enabling a pierce currentmode, wherein the controller is operative to increase the output currentfrom the zeroth level to the temporary second level, when the piercecurrent mode is enabled.